Ask the Post Office for proof of postage - you might need to prove when you sent the letter.

You can complain by email using the address listed in your supplier’s complaints procedure. If you can’t find an email address, you can call your supplier and ask them for it.

Make sure you keep a copy of any emails you send to or receive from your supplier - you might need to refer to them later.

What happens next

Your supplier will get in touch with you if they need any more details about your complaint.

They should send you a ‘decision letter’ or ‘letter of deadlock’ within 8 weeks. This explains how they’ll deal with your complaint.

If you need to take your complaint further

You can complain to the energy ombudsman after making a formal complaint if you:

you have a letter of deadlock and aren’t happy with the decision

didn’t get a decision letter or letter of deadlock within 8 weeks

The ombudsman is impartial - they’ll look into both sides of the case and make a decision. If they think your complaint was dealt with unfairly, the ombudsman can make your supplier change their decision.